How to
Boat Battery Installation and Maintenance How-To Guides
Every practical task in a marine lithium install, one task per page, each with the direct answer first and the steps underneath. The arithmetic here is the same arithmetic the calculator runs — a how-to that disagrees with the calculator would be worse than none.
- Tasks covered
- 32
- Stages
- 7
- Last reviewed
- 4 September 2026
Planning
Deciding whether to do it, and what it will cost
How to Plan a Boat Lithium Battery ConversionWork out your daily amp-hour draw first, size the bank from that, then budget the charging and protection around it — on most boats the hardware around the battery costs between a third and a half of what the battery costs.6 stepsIs a Lithium Boat Battery Upgrade Worth It? Decision GuideLithium pays for itself where you cycle the bank often and deeply — at anchor, on a liveaboard, or with a fridge running year-round. It rarely pays on a boat that sits on shore power and goes out for a day at a time.5 stepsHow to Budget a Marine Lithium Battery ConversionBudget the bank, then add the charging and protection hardware, which on most boats runs between a third and a half of the battery cost again, then add labour. Compare quotes on dollars per usable kilowatt-hour, not on label capacity.6 steps12V vs 24V Boat Electrical Systems: How to ChooseStay at 12 V unless your inverter or windlass currents are forcing cable sizes you cannot run. Twenty-four volts halves every current in the boat, but it means new chargers, a converter for 12 V accessories, and no going back cheaply.5 steps
Sizing
The arithmetic, before anyone quotes you
How to Calculate Boat Electrical Loads in Amp-HoursMultiply each load's current in amps by the hours it genuinely runs in a day, then add them up. A 5 A fridge cycling at 45% duty is 5 × 10.8 = 54 Ah, not 5 × 24.6 stepsHow to Size a Boat Lithium House Battery BankTake your daily amp-hour draw, subtract half of what your solar returns on an average day, multiply by the nights you spend away from shore power, then divide by 0.8 because you cycle lithium to 80%. Round up to a bank you can buy.6 stepsHow to Size a Marine DC-DC Battery ChargerTake the smaller of a quarter of your bank's capacity and half your alternator's rating, then round down to a charger you can buy. A 300 Ah bank behind a 90 A alternator gives min(75, 45) = 45, so a 40 A charger.6 stepsHow to Size an MPPT Solar Controller for a BoatDivide your array's watts by the bank's nominal voltage to get charge current, add headroom for a cold bright day, and buy a controller at or above that figure. 400 W on a 12.8 V bank is about 31 A, so a 30 A controller is marginal and a 40 A is not.5 stepsHow Many Solar Panels Does a Boat Need? Sizing StepsDivide the amp-hours you want solar to replace by 4.25 sun-hours and 0.75 for real-world losses, then multiply by the bank's nominal voltage to get watts. Replacing 100 Ah a day on a 12 V bank needs roughly 400 W.6 stepsHow to Size Boat Battery Cable: Current & Voltage DropSize every run for the highest sustained current that run can actually pass, then check it again for voltage drop over the round-trip length. The cable on an older boat was sized for a bank that could never deliver lithium's currents.6 stepsHow to Choose a Fuse for a Marine Lithium Battery BankFit a Class-T fuse, or an equivalent with a high interrupt rating, at each pack's positive terminal. LiFePO4 can deliver short-circuit currents in the thousands of amps, which a standard MRBF or ANL fuse may not interrupt safely.5 steps
Buying
Choosing cases, gear and the person who fits them
How to Compare Marine Lithium Battery SpecificationsCompare on dollars per usable kilowatt-hour, not on price or label amp-hours. That single figure is neutral across 12 V and 24 V cases and across chemistries, and it is the only one that reflects what you actually get.6 stepsMarine Lithium Battery Compliance Documents: What to CheckAsk for the cell and pack test certification, check the installation is covered by AS/NZS 3004.2, and confirm in writing what your insurer and marina each require before you buy.5 stepsHow to Choose a Marine Electrician for Lithium BatteriesAsk for two recent lithium installs on boats like yours, check they specify a DC-DC charger and Class-T fusing without being prompted, and confirm the quote includes commissioning and a wiring diagram.5 steps
Installing
Wiring, mounting, protecting and monitoring
How to Convert a Boat from AGM to Lithium BatteriesSize the new bank on usable capacity rather than matching the old label figure, fix the charging path before connecting anything, and replace the fusing. A straight case-for-case swap is the most common way to make this go wrong.7 stepsHow to Plan Marine Lithium House Battery Bank WiringFuse each pack at its own positive terminal, bring the packs to a common bus with equal-length cables, put the shunt on the negative between the bank and everything else, and size every run for the current the new system can pass.7 stepsHow to Install a Boat Battery Monitor and ShuntPut the shunt on the bank's negative with nothing but the battery on its battery side, run every other negative in the boat to its load side, then calibrate it at a known full charge.6 stepsHow to Wire a Marine DC-DC Battery ChargerFeed it from the cranking battery or alternator output, land its output on the lithium bank, fuse both sides close to their sources, and give it an ignition trigger so it only runs with the engine.7 stepsHow to Connect Boat Solar Panels to Lithium BatteriesWire the panels to an MPPT controller with a true lithium profile, land the controller's output on the bank through its own fuse, and connect the battery side before the panel side when commissioning.7 stepsHow to Keep a Boat Starting Battery Charged with LithiumKeep the cranking battery as a separate lead-acid battery and charge it through a DC-DC charger, a dedicated charger output, or a small trickle path — never by paralleling it with the lithium bank.5 stepsHow to Mount and Secure Lithium Batteries on a BoatMount the bank low and near the centreline, restrain it against movement in every direction including inversion, and keep the terminals covered and clear of anything metal that could fall on them.6 stepsHow to Plan Ventilation for a Boat Battery CompartmentLiFePO4 does not off-gas hydrogen in normal use the way flooded lead-acid does, so ventilation is about controlling temperature rather than venting gas — but the compartment still needs to shed heat and meet the installation standard.5 steps
Charging
Engine, solar and shore power
How to Charge Boat Lithium Batteries from an AlternatorPut a DC-DC charger between the alternator and the bank, sized to the smaller of a quarter of the bank's capacity and half the alternator's rating. Connecting a lithium bank straight to an alternator is what destroys alternators.6 stepsHow to Charge Boat Lithium Batteries from Shore PowerUse a compatible mains charger and set absorption voltage, time and float or storage behaviour to the exact battery instructions. Confirm how charging stops when the BMS requests it.6 stepsHow to Set LiFePO4 Battery Charging Voltages on a BoatTake absorption voltage, absorption time and the float or storage setting from your pack's own datasheet, and set them identically on every charging source — mains charger, solar controller and DC-DC charger.7 steps
Living with it
Reading it, storing it, and Australian heat
How to Read Lithium Boat Battery State of ChargeUse a shunt-based monitor counting amp-hours in and out. LiFePO4's voltage is almost flat between about 20% and 90%, so a voltmeter cannot distinguish a nearly full bank from a nearly empty one.6 stepsHow to Store Boat Lithium Batteries Over WinterLeave it at a partial state of charge rather than full or empty, disconnect the loads, and check it periodically. Storing LiFePO4 at 100% on a float charger for months is what ages it fastest.6 stepsLithium Boat Battery Care in Australian HeatKeep the pack out of direct engine and sun heat, check its charge and discharge temperature limits against what the compartment actually reaches, and avoid leaving it at full charge in hot weather.5 steps
Diagnosing
When it stops doing what it should
Lithium Battery BMS Disconnected? Boat Diagnosis StepsThe bank reads a normal voltage at the terminals but delivers nothing, or accepts no charge at all. Check the pack's own app or display for the cut-off reason before assuming the battery has failed.6 stepsBoat Lithium Battery Not Charging: Troubleshooting StepsWork from the source to the bank: confirm the charger is producing output, check the charge profile and voltages, look for a BMS cut-off reason, then measure voltage drop along the run.6 stepsHow to Test Lithium Boat Battery Capacity in Amp-HoursCharge it fully, then discharge at a known steady current while counting amp-hours with a shunt until the BMS cuts off or you reach the manufacturer's cut-off voltage. The amp-hours counted are the pack's real capacity.6 stepsHow to Test Voltage Drop in Boat Battery WiringMeasure voltage at the source and at the load while the circuit is carrying its full current, with the meter on the same two points the current flows between. The difference is your drop, and it only appears under load.6 steps
Elsewhere on the site